Transformer-core punching.



E. G. REED.

TRANSFORMER CORE PUNCHING.

APPLICATION FILED DEC. 26. i913.

Patented May 1, 1917.

l NTOR WITNESSES ATTORNEY.

In: News psrsns co.. Puomumm. wasnmcnml c UNITED STATES PATENT OFFICE.

EMERSON G. REED, OF WILKINSB'URG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSEELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

TRANSFORMER-CORE PUNCHING.

Application filed December 26, 1913.

To all whom it may concern: v

Be it known that I, EMERSON G. Rune, a citizen of the United States, anda resident of lVilkinsburg, in the county of Allegheny and State ofPennsylvania, have invented a new and useful Improvement in Transformer-Core Punchings, of which the following is a specification.

My invention relates to electrical transformers employed in connectionwith alternating current systems of distribution, and it has for itsobject to provide transformer core punchings of such form as to insure amaximum economy of material and a reduction in the expenses of operationand in the losses of transformers.

In the manufacture of transformers, it is highly advantageous to providecore laminations having such a form as to utilize the maximum percentageof the stock from which the laminations are to be punched. Also, it isdesirable to provide a core structure which will oii'er a minimumreluctance to the passage of the magnetic flux therethrough. Again, itis important that the laminations be formed to possess the advantage ofbeing easily assembled without tearing and cutting the coil insulationduring the assembling operation. In order to comply with theabove-mentioned require ments, I have invented laminations of a new formfor a transformer core structure which will be hereinafter fullydescribed.

In the accompanying drawing, Figure 1 is a View, in transverse section,of a transformer constructed in accordance with my invention, and Fig. 2is a view, in another transverse section, of the core structure shown inFig. 1.

Referring to Fig. 1, high-tension coils l and low-tension coils 2 areconcentrically wound and adequately insulated from one another. Afterthe coils have been assembled, the entire core structure 3 is built upto provide magnetic circuits 4:, and 6 for the flux generated by thethree groups of coils previously assembled. If the abovementionedmagnetic circuits have full crosssectional areas throughout their entirelength, it is unimportant, from the standpoint of the magneticproperties of the core, where joints 7 which are formed by abuttingedges of the laminations, are located. But, inasmuch as I have shown astructure in which the magnetic circuits comprise por- Specification ofLetters Patent.

Patented May 1, 1917.

Serial No. 808,736.

tions which have reduced cross-sectional areas, it is particularlydesirable that the air gaps formed between adjacent sections of thelaminations shall always lie in those portions of the core which havethe greater cross sectional area, as shown in Figs. 1 and 2. Bypositioning the air gaps 7 in the portions of the circuit which have afull cross sectional area, the reluctance offered to the passage of themagnetic flux across the air gaps is reduced to a minimum value becauseof the decreased flux density per unit of cross sectional area of theair gaps.

The core of my transformer comprises two similar L-shaped members 8, anL-shaped member 9 forming a central cross bar 10 which has substantiallythe same width as the outer cross-bars 11, and a rectangular member 12.It will be seen that the bars embraced by the coils are reduced in crosssectional area in order to decrease the length of the mean turn of thecoils 1 and 2. The portions of the core structure not embraced by thesaid coils are given full cross sectional areas, thereby decreasing theflux density in these portions and, consequently, the total iron losses.The magnetic fluxes generated by the current-carrying coils embracingthe bars 10 and 11 flow in the circuits a, 5 and 6, as indicated in thedrawing. The flux generated by the coils embracing the central bar 10 isdivided into two portions, one portion flowing in the circuit i and theother portion flowing in the circuit 5, the said circuits beingmagnetically connected in parallel. The fluxes generated by the coilsembracing the bars 11 are also divided into two portions, one portionflowing either in the circuit 4 or the circuit 5 in conjunction with theother portion which flows in the circuit 6. Of course, it will beunderstood that, in a three-phase transformer, as I have shown, thefluxes generated by the three groups of coils maintain the usualthree-phase relations which obtain in core structures comprising threebars each embraced by a group of coils, such being well known in theart.

It is apparent that my core structure may be easily assembled because ofthe simplicity in the form of the laminations, which require no fittingtogether of intricate parts. In building up the core structure aroundthe three groups comprising the coils 1 and 2, a plurality of punchingsare placed together to form a group of similarly laminated layers asshown in Fig. 1. When the punch ings are thus assembled, the magneticcircuit 4 comprises two air gaps 7 and the mag netic circuit 5 comprisesthree air gaps. A plurality of punchings equal in number to thoseconstituting the first group of laminations, are then placed together toform a second group of similarly laminated layers, as shown in F ig. 2.In this arrangement, the magnetic circuit 4 comprises three air gaps 7and the magnetic circuit 5 comprises two air gaps 7. In each of theabove-mentioned groups of laminated layers, the magnetic circuit 6comprises five air gaps. To balance adequately the magnetic conditionsobtaining within the transformer core and to make the reluctance of thebuilt-up magnetic circuits l and 5 as nearly equal as possible, the twoabove-mentioned groups of similarly laminated layers are alternatelyreversed with respect to each other, thereby insuring the same totalnumber of air gaps in both magnetic circuits 4 and 5 ofthe entire corestructure. As a result of placing the laminated layers so as toalternately i11- sert three air gaps and then two air gaps in each ofthe magnetic circuits 4: and 5, the magnetic reluctance of each of saidcircuits will be equivalent to that of a magnetic circuit having anumber of air gaps which corresponds to the mean between two air gapsand three air gaps. It will be seen from the foregoing description ofthe assembling operation of the core, that each of the abovementionedmagnetic circuits comprises a minimum number of air gaps which resultsin a low reluctance being ofi'ered to the flow of the magnetic fluxgenerated by the three groups of coils above mentioned. The L- plates 9constitute a portion of both magnetic circuits 4 and 5 irrespective ofwhether the transformer is of a three-phase core type, as shown, or ofthe shell type with the coils embracing only the central bars 10.

The L-plates 8 are so formed that, in conjunction with the rectangularplates 12 and the L-plates 9, a core of substantial construction isassured. At the same time, all the punchings are so simple in form thatonly a small amount of stock is wasted when the laminations are punchedfor the transformer core structure.

The forms of the several parts and the relative proportions thereof maybe varied from those here described, and, therefore, I desire that myinvention be restricted to no narrower limits than those imposed by theprior art and the demands of satisfactory service.

I claim as my invention:

1. A transformer core comprising a plurality of laminated layers eachbeing composed of three L-shaped punchings and a rectangular-shapedpunching to form three closed magnetic circuits one of which consists oftwo of said L-shaped punchings and another of which consists of thethird L- shaped punching, said rectangular-shaped punching and thelonger leg of one of the aforementioned two L-shaped punchings, saidlaminated layers being alternately reversed with respect to one another,thereby inserting in the built-up transformer core the same number ofair gaps in each of said two magnetic circuits.

2. A laminationlayer for a transformer core member comprising threeL-shaped punchings and a rcctangular-shaped punching to form a pluralityof magnetic circuits, one circuit consisting of two of said L- shapedpunchings and another consisting of the third L-shaped punching, saidrectangular-shaped punching and the longer leg of one of theaforementioned two L-shaped punchings.

In testimony whereof, I have hereunto subscribed my name this 19th dayof Dec. 1913.

EMERSON G. REED.

Witnesses:

G. G. CnownLL, B. B. HINEs.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents, Washington, D. G.

